An automatic implantable cardioverter defibrillator (AICD) or implantable cardioverter defibrillator (ICD) detects ventricular fibrillation and delivers a series of countershocks of sufficient energy to terminate the fibrillation. Such an ICD utilizes an electrode system either attached to the outer surface of the heart by means of a large surface area patch electrode, or inserted transvenously into or near the heart. Such an ICD system may be combined with a pacemaker function.
Transvenous defibrillator leads for correcting ventricular tachycardia and ventricular fibrillation include uninsulated, helically wound shocking electrodes, formed of round wire, and rely on direct contact between the electrode and tissue or blood within or near the heart to deliver electrical energy to the heart.
When the lead is implanted, the immune system of the body responds to the implant and triggers a series of biological events. As a result of this, extensive tissue ingrowth takes place, along the length of the lead, especially around the electrode. In the case of defibrillator leads, the shocking electrode is in the form of a helically wound coil, with interstices present between the individual wires that make up the coil. Due to this exposed surface area and the high energy densities seen during shocking, the tissue ingrowth problem is exacerbated. On account of the tissue ingrowth, extensive surgical intervention may be required for lead removal.